Grafted polymer composition

ABSTRACT

Aqueous emulsions of grafted polymer compositions are provided. The grafted component of these compositions has two or more polymeric substituents. The aqueous emulsions of grafted polymer compositions are particularly useful as cement modifiers.

This is a divisional of application Ser. No. 08/390,395 , filed Feb. 16,1995, now U.S. Pat. No. 5,563,187 which has been allowed.

The present invention relates to a grafted polymer composition. Inparticular, the present invention relates to polymer compositions whichhave two or more polymeric substituents grafted thereto.

Emulsion polymers are known to be useful, for example, as cementmodifiers. However, many previously known emulsion polymers intended foruse as cement modifiers suffered some drawbacks with regard to theirdispersibility or stability in the cement formulation.

One method for attempting to overcome the problem of dispersibility wasto use polyvinyl alcohol as a protective colloid during thepolymerization of the emulsion polymers as taught in Japanese PatentApplication Number Hei 2-314117. However, the high viscosity of thepolymerizations (greater than 50,000 centipoises, frequently greaterthan 100,000 centipoises) render them difficult to handle, and theparticle size of the polymers produced (greater than 50 microns) werelarger than the preferred particle size for cement modifiers.

Another attempt at overcoming the problems associated with polymericcement modifiers was to add polyvinyl alcohol to the emulsion polymersand subsequently atomizing the mixture. When polyvinyl alcohol is addedto cement modifier emulsion polymers, there is a tendency for phaseseparation. Also, the addition of polyvinyl alcohol to the emulsiontends to impart poor rheology characteristics and prolong the open timeof cement compositions containing this mixture.

The present invention seeks to overcome the problems associated withknown methods for providing redispersible polymers.

In a first aspect of the present invention, there is provided anemulsion polymer comprising a core, and grafted to said core

a) at least one graftable water-soluble polymer and at least onegraftable alkali-soluble polymer;

b) at least one graft copolymer comprising at least one graftablewater-soluble polymer grafted with at least one graftable alkali-solublepolymer;

or

c) a combination of (a) and (b).

In a second aspect of the present invention, there is provided a methodfor preparing an aqueous emulsion comprising emulsion polymerizing atleast one monomer to form a core, in the presence of

a) at least one graftable water-soluble polymer and at least onegraftable alkali-soluble polymer;

b) at least one graft copolymer comprising at least one graftablewater-soluble polymer grafted with at least one graftable alkali-solublepolymer;

or

c) a combination of (a) and (b).

In a third aspect of the present invention, there is provided a graftcopolymer comprising at least one graftable water-soluble polymergrafted with at least one graftable alkali-soluble polymer.

In a fourth aspect of the present invention, there is provided a cementcomposition comprising cement and the aqueous emulsion of the presentinvention.

Graftable water-soluble polymers are water-soluble polymers which arecapable of becoming a graft substrate for another polymer, or capable ofbeing grafted onto another polymer. Graftable water-soluble polymersuseful in the present invention include water-soluble versions of, forexample, polyvinyl alcohol, methyl cellulose, hydroxymethyl cellulose,hydroxyethyl cellulose, hydroxypropyl cellulose, starch derivatives,poly(ethylene glycol), poly(propylene glycol), poly(amino acids), otherpolycarboxylates, polyesters, polyurethanes, polyols, epoxy resins, urearesins, phenolic resins, and combinations thereof. Preferred graftablewater-soluble polymers are polyvinyl alcohol, hydroxypropyl cellulose,poly(ethylene glycol), and combinations thereof. The most preferredgraftable water-soluble polymers is polyvinyl alcohol.

When polyvinyl alcohol is used as a graftable water-soluble substrate,the polyvinyl alcohol preferably has a molecular weight of from 3,000 to100,000, more preferably from 5,000 to 50,000. It is also preferred thatwhen polyvinyl alcohol is used as a graftable water-soluble substrate,the polyvinyl alcohol is partially or fully hydrolyzed, most preferablyfrom 80 to 100 percent hydrolyzed.

Graftable alkali-soluble polymers are alkali-soluble polymers which arecapable of becoming a graft substrate for another polymer, or capable ofbeing grafted onto another polymer. Graftable alkali-soluble polymersuseful in the present invention include, for example, polymerscomprising, as polymerized units, a sufficient amount of acid-functionalmonomer, anhydride-functional monomer, salts thereof or a combinationthereof, to render the polymers alkali-soluble. Preferably, thegraftable alkali-soluble polymers comprise, as polymerized units,acid-functional monomer, anhydride-functional monomer, salts thereof ora combination thereof, at a level of from 5 to 50 percent by weight ofthe graftable alkali-soluble polymer, most preferably from 10 to 35percent by weight of the graftable alkali-soluble polymer. Preferredacid-functional monomers and anhydride-functional monomers include, forexample, acrylic acid, methacrylic acid, crotonic acid, vinylaceticacid, 2-acrylamido-2methylpropanesulfonic acid, maleic acid, maleicanhydride, itaconic acid, mesaconic acid, fumaric acid, citraconic acid,alkali metal salts thereof and ammonium salts thereof. Preferably, thegraftable alkali-soluble polymer comprises methacrylic acid.

The graftable alkali-soluble polymer further comprises, as polymerizedunits, at least one polyfunctional compound. Polyfunctional compoundsuseful for preparing the graftable alkali-soluble are selected from (i)compounds having at least two sites of ethylenic unsaturation, (ii)compounds having at least one site of ethylenic unsaturation and atleast one abstractable atom, and (iii) compounds having at least twoabstractable atoms. Such compounds, when incorporated into the graftablealkali-soluble polymer, impart one or more functional groups which arecapable of grafting onto the core polymer.

Suitable polyfunctional compounds for preparing graftable alkali-solublepolymers include, for example, ethyleneglycol dimethacrylate,diethyleneglycol dimethacrylate, triethyleneglycol dimethacrylate,polyethyleneglycol dimethacrylate, polypropyleneglycol dimethacrylate,neopentylglycol dimethacrylate, 1,3-butyleneglycol diacrylate,neopentylglycol diacrylate, trimethylolethane trimethacrylate,dipentaerythritol triacrylate, dipentaerythritol tetraacrylate,dipentaerythritol pentaacrylate, 1,3-butyleneglycol dimethacrylate,trimethylolpropane trimethacrylate, trimethylolpropane triacrylate,tripropyleneglycol diacrylate, divinyl benzene, trivinyl benzene and thelike.

Further suitable polyfunctional compounds for preparing graftablealkali-soluble polymers include, for example, allyl-, methallyl-,dicyclopentenyl-, crotyl- and vinyl esters of acrylic acid, methacrylicacid, maleic acid (mono- and di-esters), fumaric acid (mono- andall-esters) and itaconic acid (mono- and di-esters); N- or N,N di-,methallyl-, crotyl- and vinyl-amides of acrylic acid and methacrylicacid; N-methallyl and crotylmaleimide; alkenyl or cycloalkenyl esters ofacrylic acid, methacrylic acid, maleic acid (mono- and di-esters),fumaric acid (mono- and di-esters), fumaric acid (mono- and di-esters),itaconic acid (mono- and di-esters); 1,3-butadiene; isoprene; divinylbenzene; methallyl-, crotyl- and allyl-mercaptan.

Further suitable polyfunctional compounds for preparing graftablealkali-soluble polymers include, for example, allyl esters, methallylesters, vinyl esters, dicylopentenyl esters, and crotyl esters ofacrylic acid, methacrylic acid, maleic acid (mono- and di-esters),fumaric acid (mono- and di-esters) and itaconic acid (mono- anddi-esters); alkenyl and cycloalkenyl esters of acrylic, methacrylic,maleic (mono- and di-esters), fumaric (mono- and di-esters), anditaconic (mono- and di-esters) acids; allyl ether, methallyl ether,crotyl ether and vinyl ether; N-allyl amides, N,N-di-allyl amides, andvinyl amides of acrylic acid and methacrylic acid; vinyl esters of3-butenoic and 4-pentenoic acids; diallyl phthalate; triallyl cyanurate;O-allylphosphonate, methallylphosphonate, crotylphosphonate,O-alkylphosphonate, arylphosphonate, P-vinylphosphonate,P-allylphosphonate, P-crotylphosphonate, and P-methallylphosphonate;triallylphosphate, trimethallylphosphate, and tricrotylphosphate;O-vinylphosphate, O,O-diallylphosphate, dimethallylphosphate, anddicrotylphosphate; vinyl ethers and vinyl thioethers of cycloalkenolsand cycloalkene thiols; vinyl esters of cycloalkene carboxylic acids;1,3-butadiene, isoprene and other conjugated dienes; paramethylstyrene;chloromethylstyrene; allyl-, methallyl-, and crotyl-mercaptan;bromotrichloromethane; bromoform; carbon tetrachloride; and carbontetrabromide.

Preferably, polyfunctional compounds are present at a level of from 1 to25 percent by weight of the graftable alkali-soluble polymer, morepreferably from 2 to 20 percent by weight of the graftablealkali-soluble polymer. When one or more compounds having at least twosites of ethylenic unsaturation are used as the polyfunctional compound,it is preferred that said compounds having at least two sites ofethylenic unsaturation are present at a level of less than 5 percent byweight, more preferably 0.5 to 3.0 percent by weight of the graftablealkali-soluble polymer. The most preferred polyfunctional compound isallyl methacrylate.

The graftable alkali-soluble polymer may optionally comprise, aspolymerized units, at least one other monomer polymerizable with themonomers comprising the graftable alkali-soluble polymer. Preferredmonomers polymerizable with the other monomers include, for example,alkyl esters of acrylic acid, alkyl esters of methacrylic acid,hydroxyalkyl esters of acrylic acid, hydroxyalkyl esters of methacrylicadd, styrene, substituted styrenes, acrylamide, methacrylamide,substituted acrylamides and substituted methacrylamides. Preferably, thegraftable alkali-soluble polymer comprises, as polymerized units, from49 to 94 percent by weight of an alkyl acrylate or an alkylmethacrylate, most preferably methyl methacrylate.

A preferred graftable alkali-soluble polymer comprises, as polymerizedunits,

(i) acid-functional monomer, anhydride-functional monomer, salts thereofor a combination thereof, at a level of from 5 to 50 percent by weightbased on the weight of the graftable alkali-soluble polymer;

(ii) at least one polyfunctional compound at a level of from 1 to 25percent by weight based on the weight of the graftable alkali-solublepolymer; and

(iii) at least one alkyl acrylate or alkyl methacrylate at a level offrom 49 to 94 percent by weight based on the weight of the graftablealkali-soluble polymer.

The graftable alkali-soluble polymer preferably has a weight averagemolecular weight of from 1,000 to 50,000, more preferably from 2,500 to25,000. All molecular weights referred to herein and in the appendedclaims are as determined by aqueous gel permeation chromatography usinga 4,500 molecular weight poly(acrylic acid) standard.

In general, and particularly when the polyfunctional compound used inthe graftable alkali-soluble polymer has two or more sites ofethylenically unsaturation, it is desirable to use one or more chaintransfer agents to control the molecular weight when preparing thegraftable alkali-soluble polymer. The types and methods of using chaintransfer agents or mixtures thereof is well known in the art.Particularly useful chain transfer agents include, for example, C₁ -C₆alkylmercaptans and C₁ -C₆ alkyloxy mercaptans.

Monomers suitable for forming the core are any monomers capable ofundergoing an emulsion polymerization. For example, any of the monomerssuitable for use in preparing the graftable alkali-soluble polymer aresuitable for use in preparing the core. Other suitable monomers includeN,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, N-3-(dimethylamino)propyl!acrylamide, N-3-(dimethylamino)propyl!methacrylamide, tert-butylaminoethylmethacrylate, (3-acrylamidopropyl)trimethylammonium chloride,(3-methacrylamidopropyl)trimethylammonium chloride, and N-3-(dimethylamino)-2,2-dimethylpropyl!acrylamide. The selection of theparticular monomer or combination thereof, and the relative amount ofmonomers for preparing the core is not critical to the present inventionand will generally depend upon the properties sought for the applicationof the final polymer product. The selection of the monomer componentsfor preparing the core to meet desired application properties is withinthe ordinary skill of the art of preparing emulsion polymers.Preferably, the core is prepared from a combination of monomersincluding alkyl acrylates, alkyl methacrylates and combinations thereof.When the core comprises polyfunctional compounds, as described above,said polyfunctional compounds are preferably used at a level of lessthan 2 percent by weight based on the total weight of the monomers usedto prepare the core.

The process of the present invention is an aqueous emulsion process.Many aspects of emulsion polymerization are well known to those skilledin the art, such as the selection of the type and amount of initiator,the selection of the type and amount of emulsifiers (surfactants), thecontrol of pH, the rate of addition of the various components, thepolymerization temperature, the level of solids, the heating profile andthe like.

In the process of the present invention, the monomers which arepolymerized to form the core are polymerized in the presence of agrafting polymer. Grafting polymers are polymers which are capable ofundergoing a grafting reaction with the core polymer under theconditions of the emulsion polymerization of the core. Suitable graftingpolymers for the present invention include (a) a combination of at leastone graftable water-soluble polymer and at least one graftablealkali-soluble polymer; (b) at least one graft copolymer comprising atleast one graftable water-soluble polymer grafted with at least onegraftable alkali-soluble polymer; and (c) a combination of (a) and (b).

In one embodiment of the present invention, the graftable alkali-solublepolymer is itself prepared in the presence of the graftablewater-soluble polymer. By polymerizing the monomers which make up thegraftable alkali-soluble polymer in the presence of the graftablewater-soluble polymer, a graft copolymer of graftable alkali-solublepolymer and graftable water-soluble polymer is produced. In such anembodiment, the polymerization of the monomers which make up thegraftable alkali-soluble polymer are preferably polymerized in anaqueous solution of the graftable water-soluble polymer usingconventional emulsion polymerization techniques with regard to theaspects of emulsion polymerization described above. In a preferredembodiment, the monomers which make up the graftable alkali-solublepolymer are emulsion polymerized in an aqueous solution of polyvinylalcohol to prepare the graft copolymer of the present invention.

The graft copolymer preferably comprises from 50 to 90, more preferablyfrom 55 to 85, most preferably from 60 to 80 percent by weight ofgraftable alkali-soluble polymer based on the weight of the graftcopolymer. Likewise, the graft copolymer preferably comprises from 50 to10, more preferably from 45 to 15, most preferably from 40 to 20 percentby weight of graftable water-soluble polymer based on the weight of thegraft copolymer.

The monomers which make up the core can be polymerized in the presenceof the grafting polymers by (1) having the grafting polymers in thereactor prior to the addition of the monomers which make up the core,(2) adding the grafting polymers at one or more times during theaddition of the monomers which make up the core, or (3) a combinationthereof. Preferably, monomers which make up the core can be polymerizedin the presence of the grafting polymers by (1) having the graftingpolymers in the reactor prior to the addition of the monomers which makeup the core.

The grafting polymers can be unneutralized, partially neutralized orcompletely neutralized. Preferably, the grafting polymers are partiallyor completely neutralized prior to the polymerization of the core. Theneutralization can be done with any suitable base, such as alkali metalsalts, alkaline earth metal salts, ammonia, amines and combinationsthereof. Preferably, the grafting polymers are partially or completelyneutralized with a combination of alkali metal salts and alkaline earthmetal salts, most preferably with a combination of sodium salts andcalcium salts. The preferred ratio of sodium ions to calcium ions is100-0.01:1, more preferred is from 2-0.5:1, most preferred from1.5-0.6:1. Preferably, the pH of is above 7, more preferably above 8when the polymerization of the core begins. Partial or completeneutralization of the grafting copolymers prior to polymerization of thecore helps prevent agglomeration during the polymerization of the core,and improves the grafting efficiency of the grafting polymers. Thegrafting efficiency is the percentage of graft copolymer, based on thetotal amount of grafting polymer, which becomes grafted to the coreduring the polymerization of the core. The grafting efficiency isusually less than 100 percent. Thus, a portion of the grafting polymerwill remain in the aqueous phase of the emulsion. Preferably, thegrafting efficiency is at least 10 percent, more preferably at least 15percent based on the total amount of grafting polymer.

By polymerizing the monomers which make up the core in the presence ofthe grafting polymers, the emulsion polymer of the present invention isprepared. The emulsion polymer of the present invention comprises acore, and grafting polymers grafted to said core. The respective amountsof core and grafting polymer are preferably from 50 to 98 parts byweight core and from 2 to 50 parts by weight of grafting polymer, morepreferably from 70 to 95 parts by weight core and from 5 to 30 parts byweight of grafting polymer, most preferably from 75 to 90 parts byweight core and from 10 to 25 parts by weight of grafting polymer.

The emulsion polymer of the present invention has an average particlesize (diameter) less than 2 microns, more preferably less than 1.8microns, most preferably less than 1.5 microns. The particle sizesreported herein are diameters as measured by a Brookhaven BI-90 ParticleSizer which employs a light scattering technique. The emulsion polymersof the present invention are substantially spherical.

The process of the present invention provides an aqueous emulsion of thepolymers of the present invention. The aqueous emulsion is generallyfrom 25 to 70 percent by weight polymer solids, preferably from 30 to 60percent by weight polymer solids and more preferably from 35 to 55percent by weight polymer solids. Known processes which utilizepolyvinyl alcohol during the polymerization of monomers suffer fromdramatic increases in viscosity during the polymerization. Suchprocesses suffer from poor mixing, uncontrolled retention of heat anddifficult handling of the product. The process of the present invention,which utilizes a grafting polymer, allows for high solids processes atsubstantially lower viscosities. Preferably, the viscosity of theaqueous emulsion of the present invention is below 5,000 centipoises("cps"), more preferably from 50 to 2,000 cps at the more preferredlevel of polymer solids.

The emulsion polymers of the present invention are useful in the form ofan aqueous emulsion and as a dried polymer powder such as a polymerpowder prepared by spray drying. The emulsion polymers of the presentinvention are redispersible which makes them useful in many applicationssuch as redispersible cement modifiers, redispersible adhesives,redispersible coatings, redispersible films, redispersible binders forcaulks, mastics, floor polishes and the like. The emulsion polymers areparticularly useful as cement modifiers.

In each of the examples which follow, unless stated otherwise:percentages are reported as percent by weight; "Particle Size" isreported as diameter in nanometers ("nm") as measured by a BrookhavenBI-90 Particle Sizer; "Solids" were measured as the percent by weight ofa 1-2 gram sample remaining after the sample was placed in a 150° C.oven for 30 minutes; "viscosity" is reported in centipoises ("cps") asmeasured by a Brookfield viscometer using a #3 spindle at 60 revolutionsper minute ("r.p.m."); "Wet Gel" is the amount, in grams, of gellularmaterial remaining in a 150 micron screen after passing 1.0567 liters(one quart) of emulsion through the screen; "Grafting Efficiency" is thepercentage of grafting polymer grafted to the core which is determinedby subtracting from the total amount of grafting polymer the amount ofgrafting polymer which remained in the aqueous phase. To determine theamount of grafting polymer which remained in the aqueous phase, theemulsion was centrifuged at 20,000 r.p.m. for 2 hours and thesupernatant was analyzed.

EXAMPLES Example 1 Preparation of a Graft Copolymer of a GraftableAlkali-Soluble Polymer and a Graftable Water-Soluble Polymer

To a 5-liter, 4-necked round bottom flask equipped with a mechanicalstirrer, thermocouple, condenser, and nitrogen sparge was added 450grams of deionized water and 24.3 grams of Airvol™203 (polyvinyl alcoholhaving a molecular weight of from 13,000 to 23,000, 88% saponified withsodium hydroxide, available from Air Products and Chemicals, Inc.) toform an aqueous solution of a graftable water-soluble polymer. Thissolution was heated to 85° C. A monomer emulsion (ME#1) was prepared bycombining the components set forth in Table I below. An initiatorsolution was prepared by combining the components set forth in Table IIbelow. While stirring the components of the kettle, ME#1 was added tothe kettle followed by the initiator solution. After several minutes,the temperature of the kettle leveled off, a few grams of a catalystsolution containing t-butylhydroperoxide and sodium sulfoxylateformaldehyde was added to the kettle to reduce the residual monomerlevel in the graft copolymer. To the kettle was added the neutralizerslurry (as shown in Table III) to solubilize the graft copolymer.

                  TABLE I                                                         ______________________________________                                        Materials           ME #1                                                     ______________________________________                                        Deionized water     145.00                                                    sodium dodecylbenzenesulfonate                                                                    0.45                                                      Pluronic ™ L-31.sup.a                                                                          13.50                                                     Methyl Methacrylate 95.40                                                     Allyl Methacrylate  1.80                                                      Methacrylic Acid    24.30                                                     Methyl 3-mercaptopropionate                                                                       4.25                                                      ______________________________________                                         .sup.a Pluronic ™ L-31 is a block ethylene oxide/propylene oxide           copolymer available from BASF Corporation.                               

                  TABLE II                                                        ______________________________________                                        0.1 percent aqueous solution of FeSO.sub.4.7H.sub.2 O                                                    9.0    g                                           1 percent aqueous solution of ethylene diamine                                                           2.5    g                                           tetraacetic acid                                                              8.2 percent aqueous solution of t-butyl                                                                  20.4   g                                           hydroperoxide                                                                 7.9 percent aqueous solution of sodium sulfoxylate                                                       19.55  g                                           formaldehyde                                                                  ______________________________________                                    

                  TABLE III                                                       ______________________________________                                        deionized water          45.0   g                                             50 percent aqueous solution of sodium                                                                  12.2   g                                             hydroxide                                                                     Ca(OH).sub.2             5.2    g                                             ______________________________________                                    

Example 2 Preparation of an Emulsion Polymer Having a Graft CopolymerGrafted Thereto By Polymerizing in the Presence of a Graft Copolymer

A monomer emulsion (ME#2) was prepared by combining the components setforth in Table IV below. To the kettle containing the graft copolymerprepared in Example 1 was added 50.0 grams of ME#2 and 12.85 grams of a6.6 percent aqueous solution of ammonium persulfate. Alter the exothermpeaked, the remainder of ME#2 and 94.2 grams of a 4.5 percent aqueoussolution of ammonium persulfate were separately added to the kettle at aconstant rate over a period of two hours at a temperature in the rangeof 82°-86° C. The contents of the kettle temperature were thenmaintained at 82° C. for an additional fifteen minutes, then cooled to65° C. Residual monomer levels were reduced by adding a few grams of acatalyst solution containing t-butylhydroperoxide and sodium sulfoxylateformaldehyde to the kettle. The emulsion polymer of the presentinvention prepared by Example 2 is characterized in Table V below.

                  TABLE IV                                                        ______________________________________                                        Materials            ME #2                                                    ______________________________________                                        Deionized water      250.00  grams                                            Pluronic L-31        5.00    grams                                            sodium lauryl sulfate                                                                              5.00    grams                                            Butyl Acrylate       332.00  grams                                            Methyl Methacrylate  332.00  grams                                            ______________________________________                                    

                  TABLE V                                                         ______________________________________                                        Solids                  42.4                                                  Particle Size           498    nm                                             pH                      7.06                                                  Viscocity               1866   cps                                            Wet Gel                 0.4                                                   Grafting Efficiency*                                                          Graftable Alkali-Soluble Polymer                                                                      46                                                    Graftable Water-Soluble Polymer                                                                       39                                                    ______________________________________                                         *Grafting efficiency of the graft copolymer was not measured directly.   

Example 3 Polymerizing in the Presence of a Graftable Alkali-SolublePolymer and a Graftable Water-Soluble Polymer

To a 5-liter, 4-necked round bottom flask equipped with a mechanicalstirrer, thermocouple, condenser, and nitrogen sparge was added 400grams of deionized water. The water was heated to 85° C. A monomeremulsion (ME#1) was prepared by combining the components set forth inTable I above. An initiator solution was prepared by combining thecomponents set forth in Table II above. While stirring the contents ofthe kettle, ME#1 was added to the kettle followed by the initiatorsolution. After several minutes, the temperature of the kettle leveledoff, a few grams of a catalyst solution containing t-butylhydroperoxideand sodium sulfoxylate formaldehyde was added to the kettle to reducethe residual monomer level in the graft copolymer. To the kettle wasadded the neutralizer slurry (as shown in Table III above) to solubilizethe graftable alkali-soluble polymer.

To the kettle was added 24.3 grams of Airvol™203.

A monomer emulsion (ME#2) was prepared by combining the components setforth in Table IV above. To the kettle was added 50.0 grams of ME#2 and12.85 grams of a 6.6 percent aqueous solution of ammonium persulfate.After the exotherm peaked, the remainder of ME#2 and 94.2 grams of a 4.5percent aqueous solution of ammonium persulfate were separately added tothe kettle at a constant rate over a period of two hours at atemperature in the range of 82°-86° C. The contents of the kettletemperature were then maintained at 82° C. for an additional fifteenminutes, then cooled to 65° C. Residual monomer levels were reduced byadding a few grams of a catalyst solution containingt-butylhydroperoxide and sodium sulfoxylate formaldehyde to the kettle.The emulsion polymer of the present invention prepared by Example 3 ischaracterized in Table VI below.

                  TABLE VI                                                        ______________________________________                                        Solids                  41.7                                                  Particle Size           304    nm                                             pH                      7.05                                                  Viscosity               372    cps                                            Wet Gel                 0.1                                                   Grafting Efficiency                                                           Graftable Alkali-Soluble Polymer                                                                      50                                                    Graftable Water-Soluble Polymer                                                                       45                                                    ______________________________________                                    

Example 4 Polymerizing in the Presence of a Graftable Alkali-SolublePolymer and a Graftable Water-Soluble Polymer

To a 5-liter, 4-necked round bottom flask equipped with a mechanicalstirrer, thermocouple, condenser, and nitrogen sparge was added 450grams of deionized water. The water was heated to 85° C. A monomeremulsion (ME#1) was prepared by combining the components set forth inTable I above. An initiator solution was prepared by combining thecomponents set forth in Table II above. While stirring the contents ofthe kettle, ME#1 was added to the kettle followed by the initiatorsolution. After several minutes, the temperature of the kettle leveledoff, a few grams of a catalyst solution containing t-butylhydroperoxideand sodium sulfoxylate formaldehyde was added to the kettle to reducethe residual monomer level in the graft copolymer. To the kettle wasadded the neutralizer slurry (as shown in Table Ill above) to solubilizethe graftable alkali-soluble polymer.

A monomer emulsion (ME#2) was prepared by combining the components setforth in Table VII below. To the kettle was added 50.0 grams of ME#2 and12.85 grams of a 6.6 percent aqueous solution of ammonium persulfate.After the exotherm peaked, the remainder of ME#2 and 94.2 grams of a 4.5percent aqueous solution of ammonium persulfate were separately added tothe kettle at a constant rate over a period of two hours at atemperature in the range of 82°-86° C. The contents of the kettletemperature were then maintained at 82° C. for an additional fifteenminutes, then cooled to 65° C. Residual monomer levels were reduced byadding a few grams of a catalyst solution containingt-butylhydroperoxide and sodium sulfoxylate formaldehyde to the kettle.The emulsion polymer of the present invention prepared by Example 4 ischaracterized in Table VIII below.

                  TABLE VII                                                       ______________________________________                                        Materials         ME #2                                                       ______________________________________                                        deionized water   250.00                                                      Airvol ™ 203   24.30                                                       Pluronic ™ L-31                                                                              5.00                                                        sodium lauryl sulfate                                                                           5.00                                                        Butyl Acrylate    332.00                                                      Methyl Methacrylate                                                                             332.00                                                      ______________________________________                                    

                  TABLE VIII                                                      ______________________________________                                        Solids                  42.3                                                  Particle Size           173    nm                                             pH                      7.11                                                  Viscosity               298    cps                                            Wet Gel                 0.1                                                   Grafting Efficiency                                                           Graftable Alkali-Soluble Polymer                                                                      46                                                    Graftable Water-Soluble Polymer                                                                       26                                                    ______________________________________                                    

Example 5 Polymerizing in the Presence of an Unneutralized GraftableAlkali-Soluble Polymer and a Graftable Water-Soluble Polymer

To a 5-liter, 4-necked round bottom flask equipped with a mechanicalstirrer, thermocouple, condenser, and nitrogen sparge was added 450grams of deionized water. The water was heated to 85° C. A monomeremulsion (ME#1) was prepared by combining the components set forth inTable I above. An initiator solution was prepared by combining thecomponents set forth in Table II above. While stirring the contents ofthe kettle, ME#1 was added to the kettle followed by the initiatorsolution. After several minutes, the temperature of the kettle leveledoff, a few grams of a catalyst solution containing t-butylhydroperoxideand sodium sulfoxylate formaldehyde was added to the kettle to reducethe residual monomer level in the graft copolymer.

A monomer emulsion (ME#2) was prepared by combining the components setforth in Table IX below. To the kettle was added 50.0 grams of ME#2 and12.85 grams of a 6.6 percent aqueous solution of ammonium persulfate.After the exotherm peaked, the remainder of ME#2 and 94.2 grams of a 4.5percent aqueous solution of ammonium persulfate were separately added tothe kettle at a constant rate over a period of two hours at atemperature in the range of 82°-86° C. The contents of the kettletemperature were then maintained at 82° C. for an additional fifteenminutes, then cooled to 65° C. Residual monomer levels were reduced byadding a few grams of a catalyst solution containingt-butylhydroperoxide and sodium sulfoxylate formaldehyde to the kettle.When the contents of the kettle reached 45° C., the neutralizer slurry(as shown in Table III above) was added. The emulsion polymer of thepresent invention prepared by Example 5 is characterized in Table Xbelow.

                  TABLE IX                                                        ______________________________________                                        Materials           ME #2                                                     ______________________________________                                        DI water            250.00                                                    Arivol ™ 203     24.3                                                      Pluronic ™ L-31  5.00                                                      SLS                 5.00                                                      Butyl Acrylate (BA) 344.00                                                    Methyl Methacrylate (MMA)                                                                         344.00                                                    ______________________________________                                    

                  TABLE X                                                         ______________________________________                                        Solids               33.4                                                     Particle Size        ˜1.2 micron                                        pH                   7.51                                                     Viscosity            too viscous to measure                                   Wet Gel              would not filter                                         Grafting Efficiency                                                           Graftable Alkali-Soluble Polymer                                                                   38                                                       Graftable Water-Soluble Polymer                                                                    70                                                       ______________________________________                                    

Example 6 Comparative--No Graftable Water-Soluble Polymer

The procedure of Example 4 was followed except that the monomer emulsion(ME#2) was as set forth in Table XI below. The emulsion polymer preparedby Comparative Example 6 is characterized in Table XII below.

                  TABLE XI                                                        ______________________________________                                        Materials         ME #2                                                       ______________________________________                                        deionized water   250.00                                                      Pluronic ™ L-31                                                                              5.00                                                        sodium lauryl sulfate                                                                           5.00                                                        Butyl Acrylate    344.00                                                      Methyl Methacrylate                                                                             344.00                                                      ______________________________________                                    

                  TABLE XII                                                       ______________________________________                                        Solids                  45.0                                                  Particle Size           105    nm                                             pH                      7.03                                                  Viscosity               32     cps                                            Wet Gel                 2.0                                                   Grafting Efficiency                                                           Graftable Alkali-Soluble Polymer                                                                      49                                                    Graftable Water-Soluble Polymer                                                                       none                                                  ______________________________________                                    

Example 7 Comparative--No Graftable Alkali-Soluble Polymer

The procedure of Example 4 was followed except that the monomer emulsion(ME#2) was as set forth in Table XIII below. The emulsion polymerprepared by Comparative Example 6 is characterized in Table XIIV below.

To a 5-liter, 4-necked round bottom flask equipped with a mechanicalstirrer, thermocouple, condenser, and nitrogen sparge was added 600grams of deionized water and 20.0 grams of Airvol™203. The water washeated to 85° C.

A monomer emulsion (ME) was prepared by combining the components setforth in Table XIII below. To the kettle was added 50.0 grams of ME and10.4 grams of a 3.8 percent aqueous solution of ammonium persulfate.After the exotherm peaked, the remainder of ME and 94.5 grams of a 4.8percent aqueous solution of ammonium persulfate were separately added tothe kettle, at a temperature in the range of 82°-86° C., at a constantrate to provide a two hour feed time. The contents of the kettle gelledcompletely after one hour rendering further characterizationunnecessary. Residual monomer levels were reduced by adding a severalgrams of a catalyst solution containing t-butylhydroperoxide and sodiumsulfoxylate formaldehyde to the kettle.

                  TABLE XIII                                                      ______________________________________                                        Materials         ME #2                                                       ______________________________________                                        deionized water   250.00                                                      Pluronic ™ L-31                                                                              5.00                                                        sodium lauryl sulfate                                                                           5.00                                                        Butyl Acrylate    332.00                                                      Methyl Methacrylate                                                                             326.00                                                      Methacrylic acid  6.00                                                        ______________________________________                                    

The emulsion polymers prepared in Examples 2, 3, 4, 5 and 6(comparative) were evaluated as cement modifiers. In addition, Example 8(comparative) is included. Example 8 was conducted using an emulsionsample prepared according to Example 6 (comparative) to which 24.3 gramsof Airvol™203 was added. Cement mortars were prepared according to theformulation set forth in Table XIV below. The results are set forth inTable XV below.

                  TABLE XIV                                                       ______________________________________                                        Type I Portland cement                                                                        100 grams                                                     60 mesh sand    150 grams                                                     Emulsion Polymer                                                                               10 grams (based on polymer solids)                           water            40 grams (total including aqueous                                             phase of Emulsion polymer)                                   ______________________________________                                    

The following properties of the modified cements were evaluated:

Wet-out time: the time required for the mortar to reach a very workableconsistency.

Open time: a period of time that the cement mortar remains flowable andtrowelable.

Mortar rheology: mortar thickness after wet-out.

Retardation: a hardness rating evaluated by filling a 4-ounce cup withmortar, and penetrating a syringe needle into the cup after 24 hours atroom temperature.

Thin section properties: a 1/16 inch (0.16 centimeter) thickness ofmortar is placed on plywood and allow to cure for 24 hours. Toughness israted qualitatively by scratching the center with a screw driver.

                                      TABLE XV                                    __________________________________________________________________________    Example    2     3     4     5    Comp. 6                                                                            Comp. 8                                __________________________________________________________________________    Wet-out time (seconds)                                                                   15    15    15    15   15   15                                     Open time  ˜30 minutes                                                                   ˜30 minutes                                                                   ˜40 minutes                                                                   >1 hour                                                                            >1 hour                                                                            >1 hour                                Rheology   creamy                                                                              creamy                                                                              creamy                                                                              thick                                                                              v. thin                                                                            thin                                   Retardation                                                                              hard  hard  hard  med. hard                                                                          med. hard                                                                          med. hard                              Thin Section Toughness                                                                   excellent                                                                           excellent                                                                           excellent                                                                           good excellent                                                                          excellent                              __________________________________________________________________________

We claim:
 1. An emulsion polymer comprising a core and a grafted shell,said grafted shell selected from the group consisting of(a) at least onegraftable water-soluble polymer and at least one graftablealkali-soluble polymer; (b) at least one graft copolymer comprising atleast one graftable water-soluble polymer grafted with at least onegraftable alkali-soluble polymer; and (c) a combination of (a) and (b).2. The emulsion polymer of claim 1, wherein: the graftable water-solublepolymer is polyvinyl alcohol.
 3. The emulsion polymer of claim 1,wherein: the graftable alkali-soluble polymer comprises, as polymerizedunits,(i) acid-functional monomer, anhydride-functional monomer, saltsthereof or a combination thereof, at a level of from 5 to 50 percent byweight based on the weight of the graftable alkali-soluble polymer; (ii)at least one polyfunctional compound at a level of from 1 to 25 percentby weight based on the weight of the graftable alkali-soluble polymer;and (iii) at least one alkyl acrylate or alkyl methacrylate at a levelof from 49 to 94 percent by weight based on the weight of the graftablealkali-soluble polymer.
 4. The emulsion polymer of claim 1, wherein: thegrafted shell comprises from 2 to 50 percent by weight of the emulsionpolymer.
 5. A cement composition comprising cement and an aqueousemulsion comprising: water and an emulsion polymer comprising a core anda grafted shell, said grafted shell selected from the group consistingof(a) at least one graftable water-soluble polymer and at least onegraftable alkali-soluble polymer; (b) at least one graft copolymercomprising at least one graftable water-soluble polymer grafted with atleast one graftable alkali-soluble polymer; and (c) a combination of (a)and (b).
 6. A method for modifying cement compositions comprising addingto a cement composition an effective amount of an aqueous emulsioncomprising: water and an emulsion polymer comprising a core and agrafted shell, said grafted shell selected from the group consistingof(a) at least one graftable water-soluble polymer and at least onegraftable alkali-soluble polymer; (b) at least one graft copolymercomprising at least one graftable water-soluble polymer grafted with atleast one graftable alkali-soluble polymer; and (c) a combination of (a)and (b).